/* ==========================================================================
   Virtual Science期刊 — Nature 风格样式
   设计参考：Springer Nature Elements Design System (elements.springernature.com)
   与 nature.com 期刊版式：黑衬线刊名 + 深红强调 + 灰阶层级
   ========================================================================== */

:root {
  /* Nature 品牌色 */
  --n-red: #c00;
  --n-red-dark: #a50000;
  --n-red-tint: #fdf2f2;

  /* 文本色阶 */
  --n-text: #212121;
  --n-text-2: #595959;
  --n-text-3: #767676;

  /* 灰阶与背景 */
  --n-border: #d9d9d9;
  --n-border-light: #eaeaea;
  --n-bg: #ffffff;
  --n-bg-tint: #f7f7f7;
  --n-dark: #262626;

  /* 字体 */
  --font-serif: Georgia, "Times New Roman", "Noto Serif SC", "Source Han Serif SC", "STSong", "SimSun", serif;
  --font-sans: "Helvetica Neue", Helvetica, Arial, "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "Noto Sans SC", sans-serif;
}

/* ---------- 基础 ---------- */
*,
*::before,
*::after { box-sizing: border-box; }

html { -webkit-text-size-adjust: 100%; }

body {
  margin: 0;
  font-family: var(--font-sans);
  font-size: 16px;
  line-height: 1.75;
  color: var(--n-text);
  background: var(--n-bg);
}

h1, h2, h3, h4, h5, h6 {
  font-family: var(--font-serif);
  font-weight: 700;
  line-height: 1.3;
  color: var(--n-text);
  margin: 1.8em 0 0.6em;
}

h1 { font-size: 1.9rem; }
h2 { font-size: 1.5rem; }
h3 { font-size: 1.25rem; }
h4 { font-size: 1.1rem; }

p { margin: 0 0 1em; }

a {
  color: var(--n-red);
  text-decoration: none;
  transition: color 0.15s ease;
}
a:hover { color: var(--n-red-dark); text-decoration: underline; }

img { max-width: 100%; height: auto; }

hr {
  border: 0;
  border-top: 1px solid var(--n-border);
  margin: 2rem 0;
}

.skip-link {
  position: absolute;
  left: -9999px;
  top: 0;
  background: var(--n-red);
  color: #fff;
  padding: 8px 16px;
  z-index: 1000;
}
.skip-link:focus { left: 0; color: #fff; }

/* ---------- 版心 ---------- */
.wrapper {
  max-width: 1140px;
  margin: 0 auto;
  padding: 0 20px;
}

.site-main {
  min-height: 60vh;
  padding: 32px 20px 64px;
}

/* ---------- 顶部细条 ---------- */
.top-strip {
  background: var(--n-bg-tint);
  border-bottom: 1px solid var(--n-border-light);
  font-size: 13px;
}
.top-strip-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  min-height: 36px;
}
.top-strip-note {
  color: var(--n-text-3);
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}
.top-strip-links { display: flex; gap: 18px; }
.top-strip-links a { color: var(--n-text-2); }
.top-strip-links a:hover { color: var(--n-red); }

/* ---------- 刊头 ---------- */
.masthead { background: var(--n-bg); }
.masthead-inner {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  gap: 16px;
  padding-top: 26px;
  padding-bottom: 20px;
}
.masthead-logo {
  font-family: var(--font-serif);
  font-size: clamp(1.7rem, 4.5vw, 2.6rem);
  font-weight: 700;
  letter-spacing: 0.5px;
  color: #111;
  white-space: nowrap;
}
.masthead-logo:hover { color: #111; text-decoration: none; }
.masthead-logo-mark {
  display: inline-block;
  width: 0.42em;
  height: 0.42em;
  margin: 0 0.18em;
  background: var(--n-red);
  vertical-align: baseline;
}
.masthead-issue {
  margin: 0;
  color: var(--n-text-3);
  font-size: 13px;
  white-space: nowrap;
}

/* ---------- 主导航 ---------- */
.site-nav {
  border-top: 1px solid var(--n-text);
  border-bottom: 1px solid var(--n-border);
  background: var(--n-bg);
  position: sticky;
  top: 0;
  z-index: 100;
}
.nav-list {
  display: flex;
  align-items: center;
  gap: 4px;
  margin: 0;
  padding: 0;
  list-style: none;
  overflow-x: auto;
  -webkit-overflow-scrolling: touch;
}
.nav-link {
  display: block;
  padding: 12px 14px;
  font-size: 15px;
  color: var(--n-text);
  border-bottom: 3px solid transparent;
  white-space: nowrap;
}
.nav-link:hover {
  color: var(--n-red);
  text-decoration: none;
}
.nav-link.is-active {
  color: var(--n-red);
  font-weight: 600;
  border-bottom-color: var(--n-red);
}
.nav-feature { color: var(--n-text-2); }
.nav-divider {
  width: 1px;
  height: 18px;
  margin: 0 10px;
  background: var(--n-border);
  flex-shrink: 0;
}

/* ---------- 首页 ---------- */
.home-lead {
  font-family: var(--font-serif);
  font-size: 1.15rem;
  line-height: 1.8;
  color: var(--n-text-2);
  max-width: 780px;
  margin: 0 0 36px;
}

.home-grid {
  display: grid;
  grid-template-columns: minmax(0, 1fr) 300px;
  gap: 48px;
}

.section-heading {
  font-size: 1.35rem;
  margin: 0 0 8px;
  padding-bottom: 10px;
  border-bottom: 2px solid var(--n-text);
}
.section-heading-en {
  font-family: var(--font-sans);
  font-size: 0.72rem;
  font-weight: 400;
  color: var(--n-text-3);
  margin-left: 8px;
  letter-spacing: 1px;
  text-transform: uppercase;
}

/* 研究条目 */
.research-item {
  padding: 22px 0;
  border-bottom: 1px solid var(--n-border-light);
}
.research-item:last-of-type { border-bottom: 0; }

.research-label {
  display: flex;
  align-items: center;
  gap: 10px;
  margin: 0 0 8px;
  font-size: 12px;
  color: var(--n-text-3);
}
.label-tag {
  display: inline-block;
  padding: 1px 8px;
  background: var(--n-red);
  color: #fff;
  font-weight: 700;
  font-size: 11px;
  letter-spacing: 1px;
  border-radius: 2px;
}

.research-title {
  margin: 0 0 6px;
  font-size: 1.25rem;
}
.research-title a { color: var(--n-text); }
.research-title a:hover { color: var(--n-red); }

.research-standfirst {
  margin: 0 0 8px;
  color: var(--n-text-2);
  font-size: 0.95rem;
}

.research-meta {
  margin: 0;
  font-size: 0.85rem;
  color: var(--n-text-3);
}
.research-author { color: var(--n-text-2); }
.read-link { color: var(--n-red); font-weight: 500; }

/* 头条（第一条）放大 */
.research-item.is-featured { padding-top: 18px; }
.research-item.is-featured .research-title { font-size: 1.7rem; }
.research-item.is-featured .research-standfirst {
  font-size: 1.05rem;
  color: var(--n-text);
}

.research-empty { color: var(--n-text-3); padding: 32px 0; }

/* 分页 */
.pagination {
  display: flex;
  align-items: center;
  gap: 20px;
  padding: 20px 0 8px;
  border-top: 2px solid var(--n-text);
  margin-top: 12px;
  font-size: 0.9rem;
}
.pagination .page-number { color: var(--n-text-3); }

/* ---------- 侧栏 ---------- */
.home-side { padding-top: 46px; }

.side-card {
  border: 1px solid var(--n-border-light);
  border-top: 3px solid var(--n-text);
  padding: 18px 20px 20px;
  margin-bottom: 28px;
  background: var(--n-bg);
}
.side-heading {
  font-size: 1.02rem;
  margin: 0 0 10px;
  padding-bottom: 8px;
  border-bottom: 1px solid var(--n-border-light);
}
.side-card p { font-size: 0.9rem; color: var(--n-text-2); }
.side-more { font-size: 0.88rem; font-weight: 500; }

.feature-link {
  display: flex;
  align-items: center;
  gap: 14px;
  padding: 12px 14px;
  margin-bottom: 10px;
  border: 1px solid var(--n-border);
  color: var(--n-text);
  transition: border-color 0.15s ease, background 0.15s ease;
}
.feature-link:last-child { margin-bottom: 0; }
.feature-link:hover {
  border-color: var(--n-red);
  background: var(--n-red-tint);
  text-decoration: none;
  color: var(--n-text);
}
.feature-icon {
  font-size: 1.4rem;
  width: 40px;
  height: 40px;
  display: flex;
  align-items: center;
  justify-content: center;
  background: var(--n-bg-tint);
  border-radius: 4px;
  flex-shrink: 0;
}
.feature-text { display: flex; flex-direction: column; line-height: 1.4; }
.feature-text strong { font-size: 0.95rem; }
.feature-text small { color: var(--n-text-3); font-size: 0.78rem; }

.tag-cloud { display: flex; flex-wrap: wrap; gap: 8px; }
.tag-chip {
  display: inline-block;
  padding: 3px 12px;
  border: 1px solid var(--n-border);
  border-radius: 999px;
  font-size: 0.8rem;
  color: var(--n-text-2);
  background: var(--n-bg);
}
.tag-chip:hover {
  border-color: var(--n-red);
  color: var(--n-red);
  text-decoration: none;
}

/* ---------- 文章页 ---------- */
.article { max-width: 760px; margin: 0 auto; }

.breadcrumb {
  display: flex;
  align-items: center;
  gap: 8px;
  font-size: 13px;
  color: var(--n-text-3);
  margin-bottom: 24px;
}
.breadcrumb a { color: var(--n-text-3); }
.breadcrumb a:hover { color: var(--n-red); }
.breadcrumb-here { color: var(--n-text-3); }

.article-header { border-bottom: 1px solid var(--n-border); padding-bottom: 20px; }

.article-title {
  font-size: clamp(1.6rem, 4vw, 2.3rem);
  line-height: 1.25;
  margin: 10px 0 14px;
}

.article-byline {
  font-family: var(--font-serif);
  font-size: 1.02rem;
  color: var(--n-text);
  margin: 0 0 4px;
}
.article-meta {
  font-size: 0.85rem;
  color: var(--n-text-3);
  margin: 0;
}

.article-standfirst {
  font-family: var(--font-serif);
  font-size: 1.12rem;
  line-height: 1.8;
  color: var(--n-text-2);
  background: var(--n-bg-tint);
  border-left: 4px solid var(--n-red);
  padding: 16px 20px;
  margin: 24px 0 8px;
}

/* 正文 —— 衬线字体、Nature 式行距与节奏 */
.post-content {
  font-family: var(--font-serif);
  font-size: 1.02rem;
  line-height: 1.9;
}
.post-content > p,
.post-content > li { color: var(--n-text); }
.post-content p { margin: 0 0 1.15rem; }

.post-content h2 {
  font-size: 1.38rem;
  margin: 2.4rem 0 1.1rem;
  padding-bottom: 8px;
  border-bottom: 1px solid var(--n-border-light);
  line-height: 1.4;
}
.post-content h2::before {
  content: "";
  display: inline-block;
  width: 4px;
  height: 0.95em;
  margin-right: 10px;
  border-radius: 1px;
  background: var(--n-red);
  vertical-align: -0.08em;
}
.post-content h3 { font-size: 1.16rem; margin: 1.8rem 0 0.8rem; }
.post-content h4 {
  font-size: 1.02rem;
  margin: 1.4rem 0 0.6rem;
  color: var(--n-text-2);
}

.post-content pre {
  background: #1e1e1e;
  color: #d4d4d4;
  border-radius: 4px;
  padding: 1rem 1.2rem;
  overflow-x: auto;
  font-size: 0.88rem;
  line-height: 1.6;
}
.post-content pre code {
  background: none;
  padding: 0;
  color: inherit;
  font-size: inherit;
}
.post-content code {
  background: #f5f5f5;
  padding: 2px 6px;
  border-radius: 3px;
  font-size: 0.88em;
  font-family: "SFMono-Regular", Consolas, "Liberation Mono", Menlo, monospace;
}

.post-content blockquote {
  margin: 1.5rem 0;
  padding: 12px 20px;
  border-left: 4px solid var(--n-red);
  background: var(--n-bg-tint);
  color: var(--n-text-2);
}
.post-content blockquote p { margin: 0.3rem 0; }

/* 列表 */
.post-content ol,
.post-content ul { padding-left: 1.5rem; margin: 0 0 1.15rem; }
.post-content li { margin-bottom: 0.35rem; }

/* 表格 —— Nature booktabs 风格：粗顶线/粗底线，无竖线 */
.post-content table {
  width: 100%;
  border-collapse: collapse;
  margin: 0.4rem 0 1.8rem;
  font-size: 0.88rem;
  font-family: var(--font-sans);
  border-top: 2px solid var(--n-text);
  border-bottom: 2px solid var(--n-text);
}
.post-content th,
.post-content td {
  border: none;
  border-bottom: 1px solid var(--n-border-light);
  padding: 7px 10px;
  text-align: left;
  vertical-align: top;
}
.post-content thead th {
  background: transparent;
  border-bottom: 1.5px solid var(--n-text);
}
.post-content th { font-weight: 600; }

/* 插图与图注 */
.post-content img {
  display: block;
  max-width: 96%;
  margin: 1.8rem auto 0.4rem;
  border-radius: 2px;
}
.post-content .fig-caption {
  max-width: 96%;
  margin: 0 auto 1.6rem;
  font-family: var(--font-sans);
  font-size: 0.86rem;
  line-height: 1.7;
  color: var(--n-text-2);
}
.post-content .fig-caption strong { color: var(--n-text); }

/* 移动端表格横向滚动 */
@media (max-width: 640px) {
  .post-content table {
    display: block;
    width: max-content;
    max-width: 100%;
    overflow-x: auto;
  }
}

/* 关键词 */
.article-tags {
  display: flex;
  align-items: center;
  flex-wrap: wrap;
  gap: 8px;
  margin-top: 40px;
  padding-top: 20px;
  border-top: 1px solid var(--n-border);
}
.article-tags-label {
  font-size: 0.85rem;
  font-weight: 600;
  color: var(--n-text-2);
  margin-right: 4px;
}

/* 上一篇 / 下一篇 */
.article-nav {
  display: flex;
  justify-content: space-between;
  gap: 16px;
  margin-top: 28px;
}
.article-nav-link {
  display: flex;
  flex-direction: column;
  gap: 4px;
  flex: 1;
  max-width: 48%;
  padding: 12px 14px;
  border: 1px solid var(--n-border-light);
  font-family: var(--font-serif);
  font-size: 0.95rem;
  color: var(--n-text);
  line-height: 1.5;
}
.article-nav-link small {
  font-family: var(--font-sans);
  font-size: 0.75rem;
  color: var(--n-text-3);
}
.article-nav-link:hover {
  border-color: var(--n-red);
  color: var(--n-red);
  text-decoration: none;
}
.article-nav-link.is-next { text-align: right; margin-left: auto; }
.article-nav-link.is-prev { text-align: left; }
span.article-nav-link { border-color: transparent; }

/* ---------- Minima 兼容（关于 / 404 页面） ---------- */
.post { max-width: 760px; margin: 0 auto; }
.post-header .post-title {
  font-size: clamp(1.6rem, 4vw, 2.1rem);
  margin: 0 0 20px;
  padding-bottom: 14px;
  border-bottom: 1px solid var(--n-border);
}
.page-heading { font-family: var(--font-serif); font-size: 1.8rem; }
.post-list-heading {
  font-family: var(--font-serif);
  font-size: 1.4rem;
  border-bottom: 2px solid var(--n-text);
  padding-bottom: 8px;
}
.post-list { padding-left: 0; margin-left: 0; list-style: none; }
.post-list li { margin-bottom: 1.4rem; }
.post-list .post-link { font-family: var(--font-serif); font-size: 1.2rem; color: var(--n-text); }
.post-list .post-link:hover { color: var(--n-red); }
.post-meta { color: var(--n-text-3); font-size: 0.85rem; }

/* ---------- 页脚 ---------- */
.site-footer {
  background: var(--n-dark);
  color: #cfcfcf;
  margin-top: 40px;
}
.footer-grid {
  display: grid;
  grid-template-columns: 2fr 1fr 1fr;
  gap: 40px;
  padding-top: 44px;
  padding-bottom: 36px;
}
.footer-brand {
  font-family: var(--font-serif);
  font-size: 1.25rem;
  color: #fff;
  margin: 0 0 8px;
}
.footer-desc {
  font-size: 0.88rem;
  color: #a6a6a6;
  margin: 0;
  max-width: 360px;
}
.footer-heading {
  font-size: 0.8rem;
  font-weight: 700;
  letter-spacing: 1px;
  text-transform: uppercase;
  color: #8c8c8c;
  margin: 0 0 12px;
}
.footer-links {
  margin: 0;
  padding: 0;
  list-style: none;
}
.footer-links li { margin-bottom: 8px; }
.footer-links a { color: #cfcfcf; font-size: 0.9rem; }
.footer-links a:hover { color: #fff; }
.footer-bottom {
  border-top: 1px solid #3d3d3d;
  padding: 14px 0;
  font-size: 0.8rem;
  color: #8c8c8c;
}
.footer-bottom p { margin: 0; }

/* ---------- 移动端 ---------- */
@media (max-width: 960px) {
  .home-grid { grid-template-columns: 1fr; gap: 12px; }
  .home-side { padding-top: 8px; }
  .footer-grid { grid-template-columns: 1fr; gap: 24px; }
}

@media (max-width: 640px) {
  body { font-size: 15px; }
  .site-main { padding: 20px 16px 48px; }
  .masthead-inner {
    flex-direction: column;
    align-items: flex-start;
    gap: 6px;
    padding-top: 18px;
    padding-bottom: 14px;
  }
  .top-strip-note { display: none; }
  .top-strip-inner { justify-content: center; }
  .research-item.is-featured .research-title { font-size: 1.4rem; }
  .article-nav { flex-direction: column; }
  .article-nav-link { max-width: 100%; }
  h1 { font-size: 1.6rem; }
  h2 { font-size: 1.35rem; }
  h3 { font-size: 1.15rem; }
}